1. Field of the Invention
The present invention relates to a vibrator used for an angular rate sensor used for detecting a turning angular rate in a turning system and a vibratory gyroscope using the same vibrator, and particularly to a vibrator using a piezoelectric member and a vibratory gyroscope using the same vibrator.
2. Description of the Related Art
Up to now, as an angular rate sensor used for detecting a turning angular rate in a turning system, a vibratory gyroscope using a piezoelectric member has been used for detecting position of an aircraft, a ship, a space satellite, or the like. Recently, it is used in a car-navigation system, a movement detecting mechanism of a VTR or a still camera, and the like in the field of public livelihood.
Such a vibratory gyroscope utilizes the phenomenon that when an angular speed is applied to a vibrating object, a Coriolis force is generated in the direction perpendicular to the vibratory direction. Its mechanism is analyzed by using a dynamic model (for example, xe2x80x9cHandbook of Elastic Wave Device Technologiesxe2x80x9d (Danseiha-Sosi Gijutsu Handbook) issued by Ohm, Inc., pp.491 to 497). Various kinds of piezoelectric vibratory gyroscopes have been proposed up to now. For example, a Sperry tuning-fork gyroscope, a Watson tuning-fork gyroscope, a regular-triangle prism-shaped tuning-piece gyroscope, a cylindrical tuning-piece gyroscope, and the like are known as a piezoelectric vibratory gyroscope.
The inventors are studying various applications of vibratory gyroscopes, and have studied using a vibratory gyroscope as a turning rate sensor used in a car control method of an automobile body turning rate feedback system, for example. Such a system detects the direction of a steering wheel itself by a turning angle of the steering wheel. At the same time as this, the system detects the actual turning rate of the car body by means of a vibratory gyroscope. The system finds a difference between the direction of the steering wheel and the actual body turning rate by comparing them with each other, and attains a stable body control by compensating a wheel torque and a steering angle on the basis of this difference.
However, any example of the above-mentioned former piezoelectric vibratory gyroscopes can detect a turning angular rate only by arranging a vibrator in parallel with the axis of turning (what is called a vertical arrangement). The turning axis of a turning system to be measured is usually perpendicular to the gyroscope mounting part. Accordingly, in mounting such a piezoelectric vibratory gyroscope it has been impossible to shorten the piezoelectric vibratory gyroscope in height, namely, to reduce the piezoelectric vibratory gyroscope in size in the direction of the turning axis.
In recent years, a piezoelectric vibratory gyroscope capable of detecting a turning angular rate even when arranging a vibrator perpendicularly to the turning axis (what is called a horizontal arrangement) has been proposed in a Japanese laid-open publication Tokkaihei No.8-128833. In this example, as shown as an example in FIG. 1, a vibrator extends in the directions X and Y, namely, extends perpendicularly to the turning axis Z. Each of three elastic members 51a, 51b and 51c is provided with a weight 53 at one end thereof. The elastic members 51a, 51b and 51c are vibrated by piezoelectric devices 54 and 55 in the X-Y plane in phase inverse to one another. A Coriolis force in the Y direction generated by a turning angular rate xcfx89 around the Z axis is applied to the center of gravity of the weight 53. Since the plane of the elastic members 51a, 51b and 51c and the center of gravity of the weight 53 are slightly distant in the Z direction from each other, the ends of the elastic members 51a, 51b and 51c are bent reversely to one another in the Z direction by the Coriolis forces each of which is applied to the center of gravity of the weight 53. A turning angular rate xcfx89 around the Z axis is obtained by detecting this bending vibration by means of piezoelectric devices 56 and 57.
And up to now, various configurations have been known as a vibratory gyroscope using a vibrator which is composed of plural arms and a base part joining the plural arms, gives a drive vibration in a specified plane to each of the arms, and obtains a turning angular rate on the basis of a detection vibration which is perpendicular to this drive vibration and corresponds to the applied turning angular rate. For example, a Japanese laid-open publication Tokkaihei No. 7-83671 has disclosed a vibratory gyroscope using a tuning-fork vibrator made by joining three arms composed of a middle drive arm and two detection arms at both sides of the middle drive arm in one body at the base part. FIG. 2 shows a configuration of such a former vibratory gyroscope. In the example shown in FIG. 2, a vibrator 102 forming a vibratory gyroscope is composed of three arms which are composed of a middle drive arm 104 and two detection arms 103 and 105 arranged at both sides of it nearly in parallel with it, and a base 106 at which the drive arm 104 and the detection arms 103 and 105 are joined in one body with one another.
In the above-mentioned tuning-fork vibrator 102, the drive arm 104 is vibrated in the X-Z plane by an unillustrated driving means provided on the drive arm. And the left and right detection arms 103 and 105 are resonated in the same X-Z plane. When a turning angular rate xcfx89 acts around the axis Z of symmetry of the tuning-fork vibrator 102, a Coriolis force f acts on each of the detection arms 103 and 105. Since the detection arms 103 and 105 are vibrating in the X-Z plane, vibration in the Y-Z plane is induced in the detection arms 103 and 105. A turning angular rate is measured by detecting this vibration by means of an unillustrated detecting means provided on each of the detection arms 103 and 105.
A piezoelectric vibratory gyroscope disclosed in the above-mentioned Japanese laid-open publication Tokkaihei No. 8-128833 can certainly detect a turning angular rate using the Coriolis principle even when the vibrator is arranged horizontally. However, necessity of providing the weight 53 makes it insufficient to shorten the gyroscope in height. And when the weight 53 is made thin in thickness in order to sufficiently shorten it in height, moment by a Coriolis force is made small and a bending vibration is made very small, and there is a problem that a measurement sensitivity is lowered.
And in a vibrator of a piezoelectric vibratory gyroscope having the above-mentioned configuration, the drive vibration and the detection vibration are different in the vibrating direction from each other due to configuration of the vibrator. That is to say, that vibrator needs such vibrations in two directions that the elastic members 51a, 51b and 51c which are vibrating in the X-Y plane need to vibrate also in the Z direction. Generally in a piezoelectric vibratory gyroscope, it is required to keep always a constant relation between a vibration frequency for driving and a vibration frequency for detection in order to keep a good measurement sensitivity. Now, considering a single crystal as a material for a vibrator, since a single crystal is anisotropic, variation in vibration frequency caused by a temperature change varies with the direction of vibration. Therefore, attempting to form a vibrator having the above-mentioned configuration out of a single crystal causes a problem that even in case of setting a constant relation between a drive vibration frequency and a detecting vibration frequency at a certain temperature, when the temperature is changed the relation cannot be kept and the measurement sensitivity is liable to vary with temperature.
In a former vibratory gyroscope of the above-mentioned composition shown in FIG. 2, in case of forming the vibratory gyroscope by supporting the tuning-fork vibrator 102, the vibrator 102 is supported by fixing the entire end part 107 of the base part 106 of the tuning-fork vibrator 102 opposite to the end part at which the drive arm 104 and the detection arms 103 and 105 exist, or by fixing an unillustrated supporting arm at a position of this end part 107 corresponding to the axis Z of symmetry. Therefore, it cannot be said that a Coriolis force generated by a turning angular rate is efficiently utilized for action of detection vibration in the detection arms 103 and 105, and there is a problem that sharpness of resonance (Q value) of the detection vibration in the Y-Z plane in the detection arms 103 and 105 is low and the measurement sensitivity is low.
On the other hand, as a turning angular rate detecting method, both of an ordinary vibratory gyroscope having a vertically-arranged vibrator and a vibratory gyroscope having the above-mentioned horizontally-arranged vibrator electrically take in vibration of the vibrator different in mode from a drive vibration generated by a Coriolis force as displacement of a piezoceramic member, and measures a turning angular rate on the basis of the amplitude of the output signal. However, since a vibratory gyroscope having a horizontally-arranged vibrator composed of a piezoelectric single crystal has a low sensitivity to a turning angular rate due to its composition, there is a problem that it deteriorates a detection accuracy to measure a turning angular rate on the basis of the amplitude of an output signal.
In order to solve the problem of noises caused by such external factors as a voltage fluctuation, a temperature change and the like, a technique which pays attention to a fact that a phase difference between the phase of a driving signal and the phase of an output signal is changed by a Coriolis force in a vertically-arranged tuning-piece vibrator, and measures a turning angular rate on the basis of variation of the phase difference has been disclosed in Japanese patent publication Tokkohei No. 4-14734. However, even by applying the above-mentioned detection of a turning angular rate on the basis of variation in phase difference to a vibratory gyroscope having a horizontally-arranged vibrator composed of a piezoelectric single crystal, a satisfactory result cannot be obtained in measurement sensitivity and in linearity of a phase difference to a turning angular rate.
A problem the present invention attempts to solve is to make it possible to detect a turning angular rate in a sufficiently high accuracy without providing a projection having a certain weight from a vibrator toward the axis of turning even in case of setting up the vibrator in a direction in which a vibrating arm of the vibrator extends perpendicularly to the axis of turning.
Another problem the invention attempts to solve is to provide a vibrator which can be simplified in configuration, be horizontally arranged in mounting, and be reduced in height, a method for adjusting the same vibrator, and a vibratory gyroscope using the same vibrator.
An object of the invention is to provide a vibratory gyroscope capable of measuring a turning angular rate with high sensitivity by solving the above-mentioned problems.
Another object of the invention is to provide a vibratory gyroscope using a horizontally-arranged vibrator composed of a piezoelectric single crystal, the vibratory gyroscope being improved in detection accuracy of a turning angular rate.
A vibrator according to a first embodiment of the invention comprises a main arm provided with a base part and at least one bending-vibration piece extending from the base part in a direction crossing the longitudinal direction of the base part, and a fixing part for fixing one end of the base part, wherein the base part and the bending-vibration piece are formed so that they extend substantially in a specified plane.
The invention also relates to a vibratory gyroscope for detecting a turning angular rate, the vibratory gyroscope including the above discussed vibrator, an exciting means for exciting vibration of the vibrator in a plane, and a detecting means for detecting a bending vibration of the vibrator generated by a Coriolis force to be applied to the vibrator when the vibrator turns in the plane and outputting a signal according to the detected bending vibration.
Since according to the invention a drive vibration and a detection vibration of a vibrator take place in a specified plane and the invention uses a bending vibration as vibration to be detected, the invention can detect a turning angular rate with sufficiently high sensitivity without providing a projection of a certain weight from the vibrator toward the axis of turning, even when setting up the vibrator so that a vibrating arm of the vibrator extends perpendicularly to the axis of turning.
The first preferred embodiment uses a fixing piece which is fixed at both ends of it as a fixing part, and a main arm is provided at one side of this fixing piece and a resonator piece is provided at the other side of the fixing piece. The fixing piece, the main arm and the resonator piece are formed so as to extend substantially in a specified plane. That is to say, an exciting means and a bending-vibration detecting means can be disposed with a fixing piece fixed at both ends between them. Thanks to this, since such bad influences as electromechanical coupling and the like between the exciting means and the bending-vibration detecting means can be prevented, the detection accuracy is improved.
In the above-mentioned configuration, since displacement of the vibrator is in a plane, the main arm, the resonator arm, and the fixing piece can be made of the same single crystal, for example, a single crystal of quartz, LiTaO3, or LiNbO3. In this case, the measurement sensitivity can be improved. The whole of a vibrator can be made by making a single crystal thin plate and processing this single crystal thin plate by means of etching or grinding.
Although the base part and the bending-vibration piece can be made of different members from each other, it is particularly preferable that they are formed in one body. Although a material for the vibrator is not limited in particular, it is preferable to use a single crystal of quartz, LiNbO3, LiTaO3, a solid solution of lithium niobate-lithium tantalate (Li(Nb, Ta)O3, or the like. By using such a single crystal, it is possible to improve a detection sensitivity and reduce a detection noise.
And since such a single crystal is particularly insensitive to a temperature change, it is suitable for a sensor used in a car where thermal stability is necessary. This point is further described. As an angular speed sensor using a tuning-fork vibrator, there is, for example, a piezoelectric vibratory gyroscope disclosed in the above-mentioned Japanese laid-open publication Tokkaihei No. 8-128833. In such a vibrator, however, the vibrator vibrates in two directions. That is to say, in FIG. 1, the vibrator vibrates in the Z direction as well as in the X-Y plane. Therefore, particularly in case of forming the vibrator out of such a single crystal as described above, it is necessary to match the characteristics of the single crystal in the two directions with each other. In practice, however, a piezoelectric single crystal is anisotropic.
Generally in a piezoelectric vibratory gyroscope, in order to keep good sensitivity, it is required to keep a constant vibration frequency difference between a natural resonance frequency of a drive vibration mode and a natural resonance frequency of a detection vibration mode. However, a single crystal is anisotropic and a degree of variation in vibration frequency caused by a temperature change varies with the crystal face. For example, although variation in vibration frequency caused by a temperature change is very little when a single crystal is cut along a specific crystal face, variation in vibration frequency is very sensitive to a temperature change when a single crystal is cut along another crystal face.
Thus, when a vibrator vibrates in two directions, at least one of the two vibrating faces is a crystal face having a large variation in vibration frequency caused by a temperature change.
On the other hand, as shown in the invention, by making the whole of a vibrator vibrate in a specified plane and forming the vibrator out of a piezoelectric single crystal it is possible to prevent the vibrator from being influenced by anisotropy of a single crystal as described above and use only the best crystal face in characteristics of the single crystal in the vibrator.
Concretely, since every vibration of a vibrator takes place in a single plane, it is possible to manufacture a vibrator using only a crystal face having little variation in vibration frequency caused by a temperature change of a single crystal. Therefore, it is possible to provide a vibratory gyroscope having a very high thermal stability.
Among the above-mentioned single crystals, single crystals of LiNbO3, LiTaO3, and a single crystal of a solid solution of lithium niobate-lithium tantalate have particularly large electromechanical coupling coefficients. Comparing a single crystal of LiNbO3 and a single crystal of LiTaO3 with each other, the single crystal of LiTaO3 has a larger electromechanical coupling coefficient and a better thermal stability than the single crystal of LiNbO3.
A vibrator according to a second embodiment of the invention is the above-mentioned vibrator in which the main arm comprises a pair of bending-vibration pieces extending in a direction crossing the longitudinal direction of the base part and a tuning-fork vibrator piece whose tines extend respectively from the bending-vibration pieces, and the base part, the bending-vibration pieces and the tuning-fork vibrator piece are formed so as to extend substantially in a specified plane. In the above-mentioned construction, since displacement of the vibrator is in a plane, the bending vibration piece, the tuning-fork vibrator piece and the base part can be made of the same single crystal, for example, a single crystal of quartz, LiTaO3, LiNbO3, or Li(Nb, Ta)O3. This case is preferable, since the measurement sensitivity can be improved and the vibrator can be made of a single crystal thin plate by means of a wafer etching process and the like (in case of quartz) or a single crystal cutting method of grinding and the like (in case of a single crystal of LiTaO3, LiNbO3, or the like).
A vibrator adjusting method of the invention is a method for adjusting a vibrator having the above-mentioned construction, the vibrator being adjusted to a specified relation between the resonance frequency of vibration of said bending vibration piece and tuning-fork vibrator piece in said single plane and the resonance frequency of bending vibration of said base part in said single plane, by projecting both ends of said tuning-fork vibrator piece outwardly from the position of said bending vibration piece in said same single plane and reducing the length of at least one of the projected parts.
A vibratory gyroscope of this invention is a vibratory gyroscope for detecting a turning angular rate by means of a vibrator of the above-mentioned second embodiment, said vibratory gyroscope comprising an exciting means, provided in said tuning-fork vibrator piece, for exciting vibration of said tuning-fork vibrator piece, and bending vibration piece in said single plane; and a bending-vibration detecting means, provided in the base part, for detecting a bending vibration taking place in said base part in said single plane and outputting a signal according to the detected bending vibration.
And a vibratory gyroscope of this invention is a vibratory gyroscope for detecting a turning angular rate by means of a vibrator of the above-mentioned second embodiment, said vibratory gyroscope comprising an exciting means, provided in said base part, for exciting a bending movement of said base part in said single plane; and a bending-vibration detecting means, provided in the tuning-fork vibrator piece, for detecting vibration taking place in said tuning-fork vibrator piece and bending vibration piece in said single plane and outputting a signal according to the detected vibration.
A vibrator according to a third embodiment of the invention is a vibrator wherein said vibrator comprises a main arm provided with a pair of said bending-vibration pieces extending in a direction crossing the longitudinal direction of the base part and a tuning-fork vibrator piece whose tines extend respectively from the bending-vibration pieces and additionally to this main arm, a fixing piece which is fixed at both ends and at which the base part of the main arm is fixed, and a resonator piece provided on the fixing piece at a position which is at the opposite side to and corresponds to said base part, and wherein said main arm, fixing piece, and resonator piece extend in a specified plane.
It is possible to make a bending movement, having as a fulcrum the fixing piece, joined with said base part and said resonator piece take place in said base part and said resonator piece.
A vibrator adjusting method of this invention is a method for adjusting a vibrator of the third embodiment, the vibrator being adjusted to a specified relation between the resonance frequency of vibration of said tuning-fork vibrator piece and bending vibration piece in said single plane and the resonance frequency of bending vibration of said base part and said resonator piece in said single plane, by reducing length of at least one of the projected parts provided at both ends of the bending vibration pieces.
A vibratory gyroscope of this invention is a vibratory gyroscope for detecting a turning angular rate by means of a vibrator of the third embodiment, said vibratory gyroscope comprising an exciting means, provided in said tuning-fork vibrator piece, for exciting vibration of said tuning-fork vibrator piece in said single plane; and a bending-vibration detecting means, provided in the resonator piece, for detecting a bending vibration taking place in said resonator piece in said single plane and outputting a signal according to the detected bending vibration.
And a vibratory gyroscope of this invention is a vibratory gyroscope for detecting a turning angular rate by means of a vibrator of the third embodiment, said vibratory gyroscope comprising an exciting means, provided in said resonator piece, for exciting a bending movement of said resonator piece in said single plane; and a vibration detecting means, provided in the tuning-fork vibrator piece, for detecting vibration taking place in said tuning-fork vibrator piece in said single plane and outputting a signal according to the detected vibration.
In any case of the above-mentioned vibratory gyroscopes, it is possible to set an exciting means and a bending-vibration detecting means or a vibration detecting means at a position more distant from and above a vibrator in comparison with a former vibrator having no resonator piece. Accordingly, since such bad influences as electromechanical coupling and the like between the exciting means and the bending-vibration detecting means or the vibration detecting means can be prevented, the detection accuracy is improved.
A vibratory gyroscope according to a fourth embodiment of the invention is a vibratory gyroscope comprising one of said vibrators,
a driving means for driving a drive vibration,
a detecting means for detecting a vibrating state in a vibration mode which is caused by the drive vibration generated by the driving means and is different from the drive vibration, and
a phase difference detecting means for detecting a phase difference between a reference signal and an output signal, when assuming that an electrical signal used for generating a drive vibration is a reference signal and an electrical signal taken by the detecting means from a vibration having a vibration mode which is caused by the drive vibration and is different from the drive vibration;
said vibratory gyroscope detecting a turning angular rate on the basis of variation of the phase difference detected by the phase difference detecting means.
The invention has been developed by finding that in a vibratory gyroscope comprising a vibrator composed of a piezoelectric single crystal using vibration in a horizontal plane as a drive vibration, it is possible to improve detection of a turning angular rate in accuracy by obtaining a phase difference between a reference signal based on a drive vibration and an output signal based on a detection vibration, and detecting the turning angular rate on the basis of the obtained phase difference. That is to say, even in such a vibratory gyroscope as a vibratory gyroscope using a horizontally-arranged vibrator, said vibratory gyroscope being a little in vibration of the vibrator generated by a Coriolis force and low in sensitivity, it is possible to improve a gyroscopic signal to be detected in the signal-to-noise ratio of a signal to a noise caused by such external factors as a voltage fluctuation, a temperature change, and the like by using as a material for the vibrator a piezoelectric single crystal itself having a high Q value, for example, a single crystal of quartz, LiNbO3, or LiTaO3. As a result, in a range in which the amplitude of a signal called a leakage signal caused by an unnecessary vibration due to an insufficient processing accuracy or the like is 7 times larger than the amplitude of an original gyroscopic signal, it is possible to detect a turning angular rate in a range where the detection sensitivity is low but linearity of variation in phase difference to a turning angular rate is good. Therefore, the detection accuracy can be improved.
A fifth embodiment of the invention is a vibratory gyroscope having said vibrator, wherein the vibrator is a plate-shaped vibrator composed of a piezoelectric single crystal and layer-shaped parts of plural layers each of which is composed of a piezoelectric single crystal are provided between one main face and the other main face of the vibrator, and the axial directions of polarization of the respective layer-shaped parts are different from one another.
This invention relates to a vibratory gyroscope, wherein said vibrator is provided with one electrode provided on one main face and the other electrode which is provided on the other main face and is opposite to the one electrode.
This invention relates to a method for making said vibrator vibrate in a direction crossing the central face of the vibrator, said method providing one electrode on one main face, providing the other electrode opposite to the one electrode on the other main face, and applying alternating voltages different in polarity from each other, respectively, to the one electrode and the other electrode.
The invention relates to a method for detecting vibration of said vibrator, said method providing one electrode on one main face, providing the other electrode opposite to the one electrode on the other main face, connecting the one electrode and the other electrode with a voltage detecting mechanism, and detecting an alternating voltage generated between the one electrode and the other electrode by making the vibrator vibrate in a direction crossing the one main face and the other main face.
According to a vibrator and a vibratory gyroscope of the fifth embodiment, it is possible to make the vibrator perform a bending vibration in a direction crossing, preferably, perpendicular to a main face by forming electrodes on a pair of main faces of the vibrator opposite to each other and applying an alternating voltage to these electrodes. Furthermore, when a bending vibration is excited, an electric field is uniformly applied to the inside of the vibrator. Therefore, a locally ununiform electric field and an internal stress caused by the ununiform electric field are not generated inside the vibrator.
In a preferred embodiment of the invention, the respective layer-shaped parts are composed of plate-shaped members each of which is composed of a piezoelectric single crystal and which are different in the direction of polarization from one another, and these plate-shaped members are joined with one another, respectively, to form the layer-shaped parts.
And in a particularly preferred embodiment, the axial direction of polarization in one layer-shaped part of at least one main face side and the axial direction of polarization in the other layer-shaped part of the other main face side are reverse to each other.
Although a piezoelectric single crystal which is a material for the vibrator is not limited in particular, it is particularly preferable that a single crystal is quartz, lithium niobate, lithium tantalate, a solid solution of lithium niobate-lithium tantalate, langasite, or lithium tetraborate, and it is more preferable that a single crystal is lithium niobate, lithium tantalate, a solid solution of lithium niobate-lithium tantalate, or langasite. Among the above-mentioned single crystals, single crystals of quartz, LiNbO3, LiTaO3, and (Li(Nb, Ta)O3 have particularly large electromechanical coupling coefficients. Comparing a single crystal of LiNbO3 and a single crystal of LiTaO3 with each other, the single crystal of LiTaO3 has a larger electromechanical coupling coefficient and a better thermal stability than the single crystal of LiNbO3.
And it is possible to exemplify lead zirconate titanate (PZT), relaxer compounds (general expression: Pb(A1/3B2/3)O3 where A is Cd, Zn, Mg or the like, and B is Nb, Ta, W or the like), a piezoelectric single crystal of a mixed crystal system of lead zirconate titanate and a relaxer compound, langasite, and lithium tetraborate.
A vibratory gyroscope of a sixth embodiment of the invention is a vibratory gyroscope using a vibrator which is composed of plural arms and a base part for joining the plural arms with it, gives a drive vibration in a specified plane to the arms, and obtains a turning angular rate from a detection vibration corresponding to the applied angular rate of turning, said vibratory gyroscope supporting the vibrator at a small domain where there is locally a domain having the smallest detection vibration.
The invention can fix a domain where movement of the vibrator is the smallest by supporting the vibrator at a small domain where there is locally a domain having the smallest detection vibration in case of supporting the vibrator. Accordingly, since it is possible to effectively generate a detection vibration by means of a Coriolis force, a Q value of the detection vibration becomes high and the sensitivity can be improved. Since the detection vibration generated by the Coriolis force is small in amplitude, the invention is particularly effective to improve the sensitivity.
And since it increases not only the Q value of detection vibration but also the Q value of drive vibration and furthermore can improve also the sensitivity to support a vibrator at a small domain where there is locally a domain having the smallest detection vibration and a small domain where there is locally a domain having the smallest drive vibration coincide with each other, it is preferable as a preferred embodiment to support the vibrator in this way. Furthermore, it is preferable to use as a material for a vibrator a piezoelectric material such as piezoceramic or a single crystal of quartz, LiTaO3, LiNbO3, or the like, and it is more preferable in particular to use a single crystal of quartz, LiTaO3, LiNbO3, or the like. The reason is that a high Q value of a single crystal itself can be effectively used.
In the present invention, a small domain where there is locally a domain having the smallest detection vibration or the smallest drive vibration is a domain within a range where the amplitude of detection vibration or drive vibration is smaller than a thousandth of the maximum amplitude in a vibrator.
A vibratory gyroscope of a seventh embodiment of the invention is a vibratory gyroscope having a vibrator composed of an arm of a piezoelectric member, wherein said arm has a hollow part and a pair of electrodes are provided on each of the parts between which the hollow part of the arm is disposed.
In this invention, to provide a pair of electrodes on each of the parts between which the hollow part of the arm is disposed prevents an unnecessary displacement from being generated by an electric field flowing from one pair of electrodes to the other pair of electrodes, since there is no piezoelectric member at that place. Accordingly, since noises can be removed, it is possible to make a high-accuracy angular speed detection.
Although the hollow part is not limited in size in particular, it is preferable to form the hollow part equal to or longer than the electrode in the longitudinal direction of the electrode, because a leakage electric field does not cause an unnecessary displacement of the arm at all since there is no piezoelectric member to contribute the displacement. And since it is necessary to provide the hollow part correspondingly to the electrodes, it is preferable to provide the hollow part at a range of ⅓ to ⅔ arm length distant from the base of the arm in the arm of this invention which is more curved at a position closer to its base and in which each of the electrodes needs to be provided at a range of ⅓ to ⅔ arm length distant from the arm base. Furthermore, it is preferable to use a 130-degree Y plate of lithium tantalate (LiTaO3) as a piezoelectric member, since to provide the hollow part of the invention is very effective to a large influence of a leakage electric field which this invention takes as a problem.
In each of the above vibrators, its main surface may preferably have a flatness of not larger than 100 xcexcm, and an angle at the main part and the bending-vibration piece may preferably be not smaller than 45xc2x0.